1. Field of the Invention
The present invention relates to a method of inspecting the presence or absence of a residual metal film on an optically transparent multi-layer dielectric film and the degree to which the residual metal film remains, and the like. The present invention pertains to the field of optical film thickness measurement techniques.
2. Description of the Background Art
The process step of polishing a metal layer formed on a multi-layer dielectric film of a semiconductor wafer by the chemical mechanical polishing (abbreviated hereinafter as "CMP") process includes measuring and controlling the thickness of a dielectric layer (a top layer of the multi-layer dielectric film) underlying the metal layer after the metal layer is removed by the CMP process. Such film thickness control is performed, for example, when a wiring pattern is formed on the semiconductor wafer by the Damascene technique. Insufficient polishing of the metal layer by the CMP process leaves a residual metal film on the dielectric layer.
The film structure of the multi-layer film must be previously known for measurement of the thickness of each layer of the multi-layer film. Since the film structure differs depending on whether the residual metal film is present or absent, a precondition for the film thickness control after the CMP process is the detection of the presence or absence of the residual metal film. For the detection or evaluation of the degree to which the residual metal film remains on the precondition that the residual metal film is present, it is necessary to previously determine optical constants of metal required to measure the film thickness, such as a refractive index and an absorption coefficient.